Tosijs-schema is a super lightweight schema-first LLM-native JSON schema library

https://www.npmjs.com/package/tosijs-schema

46•podperson•2mo ago

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podperson•2mo ago

I wrote this library this weekend after realizing that Zod was really not designed for the use-cases I want JSON schemas for: 1) defining response formats for LLMs and 2) as a single source of truth for data structures.

7thpower•2mo ago

What led you to that conclusion?

nerdponx•2mo ago

And what makes this different? What makes it LLM-native?

podperson•2mo ago

It generates schemas that are strict by default while Zod requires you to set everything manually.

This is actually discussed in the linked article (READ ME file).

halayli•2mo ago

That's not true based on zod docs. https://zod.dev/api?id=objects

most of the claims you're making against zod is inaccurate. the readme feels like false claims by ai.

podperson•2mo ago

It seems to be true to me. And aside from the API stuff (because I am far from an expert user of Zod) all of this has been carefully verified.

dsabanin•2mo ago

Zod's validation errors are awful, the json schema it generates for LLM is ugly and and often confusing, the types structures Zod creates are often unintelligible in the and there's even no good way to pretty print a schema when you're debugging. Things are even worse if you're stuck with zod/v3

sesm•2mo ago

What's wrong with Zod validation errors?

light_hue_1•2mo ago

None of this makes a lot of sense. Validation errors are largely irrelevant for LLMs and they can understand them just fine. The type structure looks good for LLMs. You can definitely pretty print a schema at runtime.

This all seems pretty uninformed.

podperson•2mo ago

1. Zoe’s documentation, such as it is 2. Code examples

taveras•2mo ago

Happy to see more tools in the data schema space.

Will you support Standard Schema (https://standardschema.dev)? How does this compare to typebox (https://github.com/sinclairzx81/typebox)?

_heimdall•2mo ago

Had you considered using something like XML as the transport format rather than JSON? If the UX is similar to zod it wouldn't matter what the underlying data format is, and XML is meant to support schemas unlike JSON.

podperson•2mo ago

JSON Schema is a schema built on JSON and it’s already being used. Using XML would mean converting the XML into JSON schema to define the response from the LLM.

That said, JSON is “language neutral” but also super convenient for JavaScript developers and typically more convenient for most people than XML.

yeasku•2mo ago

LLMs are not people.

We want a format for LLMs or for people?

podperson•2mo ago

JSON schema is very human readable.

_heimdall•2mo ago

Why does that matter though? MCP is meant for LLMs not humans, and for something like this lib it seems the human side if the API is based on JavaScript not JSON.

drowsspa•2mo ago

As a person myself, I very much prefer JSON

_heimdall•2mo ago

MCP isn't meant for humans though, I'm not side why it matters what a human would prefer

_heimdall•2mo ago

Maybe I missed a detail here, sorry if that's the case!

Why would we need to concert XML, which already supports schemas and is well understood by LLMs, back to JSON schema?

verdverm•2mo ago

Because most of the world uses JSON and has rich tooling for JSONSchemas, notable many LLM providers allow JSONSchemas to be part of the request when trying to get structured output

_heimdall•2mo ago

LLM providers allow sending any string of text though, right? In my experience the LLM understands XML really well, though obviously that doesn't negate them from understanding JSONSchema.

verdverm•2mo ago

No, it's more than just text now, it's more than just an LLM for the most part now too. They are agentic systems with multiple LLMs, tools, and guardrails

When you provide a JSONSchemea, the result from the LLM is validated in the code between before passing on to the next step. Yes the LLM is reading it too, but non LLM parts of the system use the schema as well

This is arguably much more important for tools and subagents, but also these things are being trained with JSONSchema for tool calling and structured output

bbminner•2mo ago

While llms accept json schemas for constrained decoding, they might not respect all of the constraints.

yunohn•2mo ago

> It checks a fixed sample of items (roughly 1%) regardless of size

> This provides O(1) performance

Wouldn’t 1% of N still imply O(N) performance?

podperson•2mo ago

N is increasing. O(1) means constant (actually capped). We never check more than 100 items.

SkiFire13•2mo ago

Then it's not 1%, because if you have 100k items and you check at most 100 you have checked at most 0.1% of items.

kevmo314•2mo ago

> For large arrays (>97 items) and large dictionaries

How did we end up in a world where 97 items is considered large?

vages•2mo ago

Mind your off-by-1s: 97 items is not large, 98 is.

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Tosijs-schema is a super lightweight schema-first LLM-native JSON schema library

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